Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$227.27	8.468%	$246.5152	$246.52	$246.50	$246.50
Purchase #2	$159.87	3.304%	$165.1521	$165.15	$165.15	$165.20
Purchase #3	$180.48	8.739%	$196.2521	$196.25	$196.25	$196.30
Purchase #4	$35.48	5.838%	$37.5513	$37.55	$37.55	$37.60
Purchase #5	$9.67	12.110%	$10.841	$10.84	$10.85	$10.80
Purchase #6	$73.81	8.530%	$80.106	$80.11	$80.10	$80.10
Purchase #7	$29.83	13.246%	$33.7813	$33.78	$33.80	$33.80
7 purchase totals =	$716.41		$770.1990	$770.20	$770.20	$770.30